1. Field of the Invention
The present invention relates to a compact wide angle zoom lens.
2. Description of the Related Art
As a wide angle zoom lens widely used on single-lens reflex cameras, a 4-group zoom lens includes sequentially from an object side, lens groups having negative, positive, negative, and positive refractive powers, respectively (see, for example, Japanese Patent Laid-Open Publication Nos. 2006-276452 and 2006-39531, and Japanese Patent No. 3391883).
The zoom lenses recited in Japanese Patent Laid-Open Publication Nos. 2006-276452 and 2006-39531, and Japanese Patent No. 3391883 respectively include sequentially from the object side, lens groups having negative, positive, negative, and positive refractive powers, respectively and are capable of 1.5× or greater zoom. The zoom lens recited in Japanese Patent Laid-Open Publication No. 2006-276452, secures an angle of view on the order of 80 degrees at the wide angle edge, and is capable of 2.8× zoom. The zoom lens recited in Japanese Patent Laid-Open Publication No. 2006-39531, secures an angle of view on the order of 105.8 degrees at the wide angle edge, and is capable of 1.95× to 2.36× zoom. The zoom lens recited in Japanese Patent No. 3391883 secures an angle of view on the order of 99 degrees at the wide angle edge, and is capable 1.85× zooming.
As with the zoom lenses recited in Japanese Patent Laid-Open Publication Nos. 2006-276452 and 2006-39531, and Japanese Patent No. 3391883, conventional wide angle zoom lenses, in general, have aspheric surfaces formed on multiple surfaces of the lenses configuring a first lens group, to achieve both correction of prominent aberration consequent to increasing the angle of view at the wide angle edge and a reduction of the size of the first lens group. In particular, a large-diameter, aspheric glass lens is employed for the lens disposed farthest on the object side of the zoom lens.
In the zoom lens recited in Japanese Patent Laid-Open Publication No. 2006-276452, an aspheric lens having a strong negative refractive power is disposed farthest on the object side of the zoom lens, and the zoom lens suppresses the effective diameter of the front frame and secures high imaging performance at wide angles. However, this zoom lens has a narrow angle of view on the order of 80 degrees at the wide angle edge and meeting demands for a wider angle of view is difficult. In addition, since the glass lens disposed farthest on the object side is aspheric, a problem of extremely high manufacturing cost arises.
The zoom lenses recited in Japanese Patent Laid-Open Publication No. 2006-39531 and Japanese Patent No. 3391883, both have an aspheric lens of a strong negative refractive power disposed farthest on the object side and are designed to achieve both an ultra wide angle and reduction of the front frame. Although these zoom lenses both have angles of view on the order of 100 degrees at the wide angle edge and are designed to achieve sufficiently wide angles, the first lens group is large and thus, are not suitable for imaging apparatuses of which compactness is strongly demanded of late. In addition, since the glass lens disposed farthest on the object side of the zoom lens is aspheric, a problem of extremely high manufacturing cost further arises.